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      <p>Many disk drives contain onboard caches.  Some of these drives include
battery-backup or other functionality that guarantees that all cached
data will be completely written if the power fails.  These drives can
offer substantial performance improvements over drives without caching
support.  However, some caching drives rely on capacitors or other
mechanisms that guarantee only that the write of the current sector
will complete.  These drives can endanger your database and potentially
cause corruption of your data.</p>
      <p>To avoid losing your data, make sure the caching on your disk drives is
properly configured so the drive will never report that data has been written
unless the data is guaranteed to be written in the face of a power failure.
Many times, this means that write-caching on the disk drive must
be disabled.</p>
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